Desanding apparatus and system

ABSTRACT

A desanding vessel is inserted in a high velocity fluid stream containing entrained particulates. The vessel comprises an upper freeboard portion having a large cross-sectional wherein the fluid stream velocity drops and particulates fall from suspension. Preferably the fluid stream is introduced offset upwardly from an axis of a horizontally oriented cylindrical vessel, released particulates falling to accumulate in a lower belly portion. The freeboard portion is maintained using a depending flow barrier adjacent the vessel&#39;s outlet which sets the depth of accumulation in the belly portion. A cleanout enables periodic removal of accumulations.

CROSS REFERENCE TO RELATED APPLICATION

This application is a divisional application of U.S. application Ser.No. 10/668,266 filed Sep. 24, 2003 now U.S. Pat. No. 6,983,852 andclaiming priority of U.S. Provisional application 60/417,146 filed Oct.10, 2002 and of prior foreign applications namely, Canadian PatentApplication 2,407,554 filed Oct. 10, 2002 and Canadian PatentApplication 2,433,741 filed Jun. 27, 2003.

FIELD OF THE INVENTION

The present invention relates to a system and apparatus for the removalof particulates such as sand from fluid streams produced from a wellwhile minimizing abrasion of the involved equipment.

BACKGROUND OF THE INVENTION

Production from wells in the oil and gas industry often containparticulates such as sand. These particulates could be part of theformation from which the hydrocarbon is being produced, introducedparticulates from hydraulic fracturing or fluid loss material fromdrilling mud or fracturing fluids or from a phase change of producedhydrocarbons caused by changing conditions at the wellbore (Asphalt orwax formation). As the particulates are produced, problems occur due toabrasion, and plugging of production equipment. In a typical startupafter stimulating a well by fracturing, the stimulated well may producesand until the well has stabilized, often up to a month after productioncommences. Other wells may require extended use of the desander 10.

In the case of gas wells, fluid velocities can be high enough that theerosion of the production equipment is severe enough to causecatastrophic failure. High fluid stream velocities are typical and areeven purposefully designed for elutriating particles up the well and tothe surface. An erosive failure of this nature can become a serioussafety and environmental issue for the well operator. A failure such asa breach of high pressure piping or equipment releases uncontrolled highvelocity flow of fluid which is hazardous to service personnel. Releaseto the environment is damaging to the environment resulting in expensivecleanup and loss of production. Repair costs are also high.

In all cases, retention of particulates contaminates both surfaceequipment and the produced fluids and impairs the normal operation ofthe oil and gas gathering systems and process facilities.

In one prior art system, a pressurized tank (“P-Tank”) is placed on thewellsite and the well is allowed to produce fluid and particulates. Thefluid stream is produced from a wellhead and into a P-Tank until sandproduction ceases. The large size of the P-Tank usually restricts themaximum operating pressure of the vessel to something in the order of1,000-2,100 kPa. In the case of a gas well, this requires some pressurecontrol to be placed on the well to protect the P-Tank. Further, for agas well, a pressure reduction usually is associated with an increase ingas velocity which in turn makes sand-laden wellhead effluent much moreabrasive. Another problem associated with this type of desandingtechnique is that it is only a temporary solution. If the well continuesto make sand, the solution becomes prohibitively expensive. In mostsituations with this kind of temporary solution, the gas vapors are notconserved and sold as a commercial product.

An alternate known prior art system includes employing filters to removeparticulates. A common design is to have a number of fiber-mesh filterbags placed inside a pressure vessel. The density of the filter bagfiber-mesh is matched to the anticipated size of the particulates.Filter bags are generally not effective in the removal of particulatesin a multiphase conditions. Usually multiphase flow in the oil and gasoperations is unstable. Large slugs of fluid followed by a gas mist iscommon. In these cases, the fiber bags become a cause a pressure dropand often fail due to the liquid flow therethrough. Due to the highchance of failure, filter bags may not be trusted to remove particulatesin critical applications or where the flow parameters of a well areunknown. An additional problem with filter bags in most jurisdictions isthe cost associated with disposal. The fiber-mesh filter bags areconsidered to be contaminated with hydrocarbons and must be disposed ofin accordance to local environmental regulation.

Clearly there is a need for more versatile and cost effective system ofparticulate handling.

SUMMARY OF THE INVENTION

Desanding apparatus is provided which is placed adjacent to a well'swellhead for intercepting a fluid stream flow before prior to entry toequipment including piping, separators, valves, chokes and downstreamequipment. The fluid stream can contain a variety of phases includingliquid, gas and solids.

In one embodiment, a pressure vessel is inserted in the flowsteam byinsertion into high velocity field piping extending from the wellhead.The vessel contains an upper freeboard portion having a cross-sectionalarea which is greater that of the field piping from whence the fluidstream emanates. As a result, fluid stream velocity drops andparticulates cannot be maintained in suspension. A cross-sectional areaof the freeboard portion is maintained through a downcomer flow barrieradjacent the vessel's exit.

In a broad aspect, desanding apparatus vessel for removal ofparticulates from a fluid stream containing particulates comprises: afluid inlet adjacent a first end of the vessel and adapted for receivingthe fluid stream, the fluid inlet discharging the fluid stream at aninlet velocity into a freeboard portion at a top of the vessel, thefluid stream in the freeboard portion having an elutriation velocityless than the inlet velocity and such that contained particulates have afall trajectory; a fluid outlet from the vessel, the outlet being spacedhorizontally from the inlet; and a flow barrier depending from the topof the vessel and having a lower edge so as to direct the fluid streambelow the barrier before discharge from the outlet port for maintainingthe freeboard portion above the lower edge and forming a belly storageportion below the lower edge, the flow barrier being positioned betweenthe fluid inlet and fluid outlet and the flow barrier being spaced fromthe fluid inlet so as to enable the fall trajectory of a substantialamount of the particulates to intersect the belly portion so asaccumulate particulates in the belly portion prior to the flow barrierwherein the fluid stream at the fluid outlet is substantially free ofparticulates.

Preferably, the flow barrier is a depending weir independent of theoutlet, or could be formed by the outlet itself. A cleanout port ispreferably included for periodic removal of accumulations ofparticulates.

More preferably, a vessel of an embodiment of the present invention isincorporated in a desanding system to replace existing prior connectivepiping, the vessel being supported using structure to align the vesselwith the wellhead piping and downstream equipment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 a is a schematic arrangement of connective wellsite piping of theprior art;

FIG. 1 b is a schematic arrangement of one embodiment of the inventionhaving been installed in place of the prior connective wellsite pipingof FIG. 1 a;

FIG. 2 a is an exploded view of the inlet to one embodiment of thevessel of the invention which illustrates a nozzle arrangement in aneccentric vessel inlet;

FIG. 2 b is an exploded view of the inlet to one embodiment of thevessel of the invention which illustrates a nozzle arrangement adaptedto a blind flange;

FIG. 3 is a cross-sectional side view of one embodiment of the inventionillustrating fluid streams, falling trajectory of particulates, andaccumulations of separated liquid, particulates and particulate-freefluid discharge;

FIGS. 4 a through 4 c illustrate a variety of optional flow barriersapplied at the fluid outlet; and

FIG. 5 is a performance graph of the achievable gas throughout rates atvarious pressures while still achieving particulate removal for apessimistic case of a fluid stream containing fine 100 mesh sand.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As shown in FIGS. 1 b and 3, a desander 10 comprises a substantiallyhorizontal, cylindrical pressure vessel 11 having a first fluid inletend 12 adapted for connection to a fluid stream F such as from wellheadpiping 9 and a fluid outlet 13 connected to downstream equipment 14 suchas multiphase separators. The fluid stream F typically comprises avariety of phases including gas G, some liquid L and entrainedparticulates such as sand S. The fluid stream emanating from the fluidoutlet 13 is typically liquid L and gas G, with a substantial portion ofthe particulates S being captured by the desander 10. As a system, thedesander 10 is typically inserted as a replacement for existing piping15 (shown in FIG. 1 a). The desander 10 is preferably supported withstructure 16 such as elevation adjustable jacks to align the desander 10relative to the existing wellhead piping 9 and downstream equipment 14.

With reference to FIGS. 2 a and 2 b, the inlet 12 is fitted with a firstconnector or inlet flange 20 so as to better facilitate installation, toallow easy inspection for wear, to minimize equipment erosion and tosimplify replacement when erosion has reduced material thicknesses toacceptable minimums. A nozzle 21 and a second connector or a nozzleflange 22 are adapted for complementary and sealed connection to theinlet flange 20. Typically, the nozzle 21 has a threaded inlet 23 whichis adapted for threaded connection to an existing coupling 24 from thewellhead piping 9. The nozzle inlet 23 is threaded onto the coupling 24and the vessel and inlet 12 is positioned over the nozzle 21 and theflanges 20,22 are connected.

In greater detail as shown in FIGS. 2 a, 2 b and 3, the nozzle 21 has aprotruding discharge portion 25 which extends adjacent the top of thevessel 11. The inlet 12 is offset upwardly from an axis A of the vessel11 and extends into an upper freeboard portion 30. Preferably, as shownin FIG. 2 a, an eccentric fitting 31 is applied to the inlet 12. Whencoupled with the inlet flange 20 on the eccentric fitting 31, the nozzle21 is shifted upwardly from an axis A of the vessel 11. Similarly, asshown in FIG. 2 b, the nozzle 21 can extend through a large blind inletflange 20 fit directly to the vessel 11 positioned so as to be shiftedupwardly from an axis A of the vessel 11. The nozzle 21 discharges thefluid stream F along the nozzle's axis, a path P, substantially parallelto the vessel's axis A. The nozzle inlet 23 is typically formed ofheavy-wall piping to extend its operational life in the abrasiveenvironment of the particulate laden fluid stream F. Further, thenozzle's discharge 25 protrudes into the vessel 11 sufficiently toextend beyond the inlet 12 and into the freeboard portion 30, therebyaiding in minimizing localized wear on the less easily replaced inlet12, or eccentric fitting 31, of the vessel 11

In FIG. 3, the desander 10 further comprises belly portion 32, formedbelow the freeboard portion 30, for receiving and temporarily storingliquids L and sand S which separate from the fluid stream F. The fluidstream F containing sand S enters through the inlet 12 and is receivedby a larger cross-sectional area and substantially gas-phase volume ofthe freeboard portion 30. Accordingly, the velocity of the fluid streamF slows to a point below the entrainment or elutriation velocity of atleast a portion of the particulates S in the fluid stream. Those ofskill in the art are able to determine and apply the parameters of thefluid stream F, fluid stream velocity and those of the particulates S soas to determine the elutriation characteristics. As the area of thefreeboard portion 30 increases, the velocity of the fluid stream F slowsand a lesser fraction of the particulates remain entrained; a greaterfraction of particulates S falling out of suspension from the fluidstream F. The particulates S are discharged horizontally from the nozzle21 along path P, and as they fall from suspension, they adopt adownwardly curved trajectory under the influence of gravity. Preferably,to avoid impingement-type erosion, the length of the vessel issufficient to permit the particulates to fall out of suspension beforeimpinging internals of the vessel 11. Given sufficient horizontaldistance without interference, the particulates S eventually fall fromthe freeboard portion 30 and the trajectory intersects with the bellyportion 32. The particulates S deposit and accumulate over time in thebelly portion 32. Typically, liquids L from the fluid stream alsocollect in the vessel's belly portion 32.

The freeboard portion 30 is maintained using means such as a dependingflow barrier 40 to ensure that the collected liquids L and particulatesS only reach a maximum depth in the belly portion 32 of the vessel 11. Aminimum cross-section area of the freeboard portion and preferred lengthof the freeboard portion 30 are determinable based on the elutriationcharacteristics and are established so as to maximize release of theparticulates S before they reach the outlet 13. The greater the lengthor spacing between the inlet 12 and the flow barrier 40, the greater isthe opportunity to drop and release entrained particulates S.

Typically, liquid L out of the fluid stream F accumulates in the bellyportion 32 to a steady state level and then is re-entrained fordischarge with fluids exiting the outlet 13 without affecting thecapability of the vessel 11 and belly portion 32 to continue toaccumulate particulates S. Regardless of dropout of liquids L from gas Gand collection of liquid L in the vessel 11, this upper freeboardportion 30 remains substantially gas-filled. However, should a maximumdepth of particulates S be reached during operation and encroach on thefreeboard portion 30, operations may yet continue as if the vessel 11were not even installed; both incoming liquid L and particulates S beingtemporarily re-entrained with the fluid stream flowing from the vesseloutlet 13 until the earliest opportunity to perform maintenance.Typically the belly portion 32 vessel 11 is periodically cleaned out oremptied of accumulated particulates and liquid at sufficient intervalsto ensure that the maximum accumulated depth does not encroach on thefreeboard portion 30. Maintenance and operations personnel are furtherable to physically view sand production volumes during the cleanout andinspection.

The flow barrier 40 depends downwardly from the top of the vessel 11.The flow barrier 40 has a lower edge 41 which sets the maximum depth ofthe belly portion 32. As discussed above, the flow barrier 40 ispreferably spaced sufficiently from the inlet 11 to enable the falltrajectory of the particles to intersect the belly portion 32 beforeimpinging on the flow barrier 40 itself.

As shown in FIGS. 4 a-4 c, the flow barrier 40 can comprise a discreteor separate plate 40 a, 40 b as shown in FIGS. 4 a and 4 b, spaced fromthe outlet 13, or as shown in FIG. 4 c, a flow barrier 40 c can beformed by the outlet 13 itself. All of the various flow barriers 40,40a, 40 b, 40 c have a lower edge 41 which forces the fluid stream Sthereunder before discharging from the vessel 11 at outlet 13.Accumulated levels L,S encroaching above the lower edge 41 will resultin high velocities and re-entrainment of liquids L and particulates Sfrom the area about the flow barrier 40, inherently resulting in asteady state maximum level of accumulation of the belly portion 32.

In the embodiment shown in some detail in FIG. 4 c, the outlet 13 itselfacts as the flow barrier 40, which incorporates a tubular portion 43protruding downwardly and depending through the freeboard portion 30.The tubular portion 43 also has a lower edge 41 spaced from the top ofthe vessel 11 which forces the fluid stream F to exit from a pointnearer the vessel axis A. Particulate-free fluid, typically being gas Gand some liquid L, is collected about the axis A for discharge throughthe discharge tubing 40 and outlet 13. An advantage of providing aseparate flow barrier 40,40 a, 40 b is that any abrasion and erosion isborne by the barrier 40 and not by the outlet's 13 tubular portion 43.

As shown in FIGS. 4 a, 4 c, the outlet 13 for the vessel 10 ispreferably arranged perpendicular to the axis A of the vessel 10 forfurther inertial rejection of re-entrained particulates S.

Referring once again to FIG. 3, a quick release pressure-vesselcompatible cleanout 50 is provided for access to the vessel 11 forcleanout of the accumulated particulates. The vessel must bedepressurized before opening and cleaning out particulates. Typically,mechanically-interlocked safety means 51 are provided so that the vesselmust be de-pressurized before the cleanout can be opened. Forde-pressurization, the vessel is isolated from the fluid stream F andpressure is bled off from the freeboard portion 30 until the cleanout 50be removed. As shown in FIG. 1 b, a catch basin 52 or other suitablecollection means is provided for accepting the collected liquid L andparticulates S. Manual cleanout is performed although automated cleanoutcould be incorporated without diverging from the intent of theinvention.

EXAMPLES

A typical vessel according to the present invention, and for referenceare roughly approximated by the proportions of FIG. 3, can be a 6″ or an8″ diameter. Using an 8″ diameter, schedule 160 shell for the vessel 11can result in a fluid stream capacity of about 8 million cubic feet ofgas per day. A 2″ schedule 160 inlet nozzle extends about 1″ beyond aneccentric inlet 12 and into the vessel 11. With a flow barrier 40 placedabout 8 feet from the nozzle discharge 25, the desander 10 achieved acorresponding and typical collection rate of 1.5 gallons of sandparticulates per day, determined in a worst case scenario of particlesof about 100 mesh. Applied to problem wells in several exceptionalcases, using no vessel at all, one prior art wellhead, piping andequipment experienced four breaches and in another case, seven breaches.After installation of a preferred vessel of the present invention, nofurther breaches were experienced. In one case, the resulting collectionof particulates, as sand, was about 5 liters per day.

Further, as shown in FIG. 5, the throughput capability of 8 inch and 10inch diameter desanding vessels are illustrated for a variety of fluidpressures.

A system incorporating a desanding apparatus according to one of theembodiments disclosed herein will benefit from advantages including: Asa desander 10 is more cost effective than a “P Tank”, the desander canbe economically placed on a wellsite for long term sand protection(substantially permanent as required); with a pressure rating thatallows the vessel to operate at the wellhead conditions, minimalpressure drop is experienced across the vessel; the desander is designedto exceed ASME code for pressure vessels; sand is removed from the fluidstream without erosive effects on the operator's downstream equipmentand; as the vessel is passive, having no moving parts, plugging fromparticulates is not an issue; sand can be removed simply andmechanically from the vessel at regular intervals; by removing the sandprior to it entering the producing system, contamination of equipmentand produced fluids is avoided; and the desander is capable of handlingmultiphase production and has demonstrated an ability to remove sandfrom both gas and oil streams. This results in a wider application thanprior art filter methods.

1. In a horizontal, cylindrical desanding vessel having a vessel inletadjacent a first end of the vessel for receiving a fluid streamcontaining particulates, the fluid inlet discharging the fluid stream atan inlet velocity into a freeboard portion at a top of the vessel, thefluid stream in the freeboard portion having an elutriation velocityless than the inlet velocity such that the contained particulates have afall trajectory therein and a fluid outlet from the freeboard beingspaced horizontally from the inlet, the improvement comprising a nozzlecomprising: an inlet formed at a first end of the nozzle for connectionto a source of the fluid stream; and a protruding discharge formed at asecond end of the nozzle which when connected to the vessel inlet,extends sufficiently from the vessel inlet for discharging the fluidstream into the freeboard portion of the vessel away from the vesselinlet so as to minimize erosion thereto, wherein the fluid stream isdischarged along a path being substantially parallel to a vessel axisfor discharge of the fluid stream and particulates into the freeboardportion of the vessel.
 2. The nozzle of claim 1 wherein the vessel inletfurther comprises a first connector, the nozzle further comprising: anozzle flange adapted for connecting to the first connector.
 3. Thenozzle of claim 2 wherein the first connector is an inlet flange.
 4. Thenozzle of claim 2 wherein the first connector is a blind inlet flangefit to the vessel for shifting the nozzle upwardly from the vessel'saxis.
 5. The nozzle of claim 1 further comprising: an eccentric fittingapplied to the vessel's inlet and positioned between the vessel inletand a first connector for aligning the nozzle offset above the vessel'saxis.
 6. The nozzle of claim 5 wherein the first connector is an inletflange.
 7. The nozzle of claim 5 wherein the first connector is a blindinlet flange fit to the vessel for shifting the nozzle upwardly from thevessel's axis.
 8. The nozzle of claim 1 wherein the nozzle isreplaceably connected to the vessel inlet.
 9. The nozzle of claim 1wherein the first end of the nozzle is threaded for connection to thesource of the fluid stream.
 10. A replaceable nozzle system for ahorizontal, cylindrical desanding vessel comprising, in combination: ahorizontal, cylindrical desanding vessel having a vessel inlet adjacenta first end of the vessel for receiving a fluid stream containingparticulates, the fluid inlet discharging the fluid stream at an inletvelocity into a freeboard portion at a top of the vessel, the fluidstream in the freeboard portion having an elutriation velocity less thanthe inlet velocity such that the contained particulates have a falltrajectory therein and a fluid outlet from the freeboard being spacedhorizontally from the inlet; and a nozzle comprising: an inlet formed ata first end of the nozzle for connection to a source of the fluidstream; and a protruding discharge formed at a second end of the nozzleso as when connected to the vessel inlet the protruding dischargeextends sufficiently outwardly from the vessel inlet for discharging thefluid stream into the freeboard portion of the vessel away from thevessel inlet so as to minimize erosion thereto, wherein the fluid streamis discharged along a path being substantially parallel to a vessel axisfor discharge of the fluid stream and particulates into the freeboardportion of the vessel.
 11. The nozzle system of claim 10 wherein thevessel inlet further comprises a first connector and the nozzle furthercomprises a nozzle flange for connecting to the first connector.
 12. Thenozzle of claim 11 wherein the first connector is an inlet flange. 13.The nozzle of claim 11 wherein the first connector is a blind inletflange fit to the vessel for shifting the nozzle upwardly from thevessel's axis.
 14. The nozzle system of claim 10 further comprising: aneccentric fitting applied to the vessel's inlet and positioned betweenthe vessel inlet and a first connector for aligning the nozzle offsetabove the vessel's axis.
 15. The nozzle of claim 14 wherein the firstconnector is an inlet flange.
 16. The nozzle of claim 14 wherein thefirst connector is a blind inlet flange fit to the vessel for shiftingthe nozzle upwardly from the vessel's axis.